Here's The deal. To me that makes no sense. I have a degree in auto body paint and repair and let me tell you this. The color of a car is not painted on bare metal neither is color painted on bare fiberglass. The color is painted on top of a product called sealer. This is a barrier that actually seals of the rest of the car so that there is no reaction between chemicals and so that any repair spots or imperfection do not bleed though. New cars are painted with this along with other layers of different protection. So if all the parts are sealed with sealer which they are will be the same because it is not painted on fiberglass nor metal but sealer. So the real reason for the mismatchis because the bumper and the car were not painted at the same place not at the same time. The bumpers come perpainted by a different contractor. Even though they use the same paint they do not use the same machine or the same spray pattern and that can cause a paint difference. Its common on newer cars and it can be fixed by painting the whole car correctly.
yeah, i tried to explain that to a guy who "did body work" but he insisted that plastic and metal make the color look different... not if you use sealer and prep anywhere near right.
i saw a brand new fiesta with totally different bumpers and mirrors from the rest of the car. why? the plastic stuff is painted in another location at another time and since its a fancy tricoat (and yellow) that crap is ridiculously hard to match. this is a reason why i'd be very hesitant to order a yellow car. my buddy's SER sentra was the same way.